THE RENAL CIRCULATION 



! 473 



FIG. 19. The countercurrent mechanism 

 during diuresis (absence of ADH action). 

 [After VVirz (349).] 



table 2. Distribution of Cells and Plasma in Zones of the Kidney 



All values as ml/100 g. [After Lilienfield el at. (,186).] 



to an erroneous impression of a larger volume of 

 distribution for those substances which are bound by 

 albumin. It is noteworthy that red cell volumes per 

 gram of tissue are very similar in the medulla and 

 the outer cortex (84), so that the low apparent hema- 

 tocrit in the medulla is the result of the large "ap- 

 parent" albumin space. 



Confirmation of the high concentration of albumin 

 in the loops of the vasa recta would lead to the in- 

 teresting possibility of a countercurrent system for 

 accumulation of albumin in the papillary portion 

 of the loops. High concentration of albumin here 

 would aid the rapid net transport of water from the 

 interstitial space into the zone of elevated oncotic 

 pressure, facilitating removal by the vascular system. 

 The countercurrent exchange of water would begin 

 at the juxtamedullary portion of the vasa recta by 

 movement of water across to the ascending venae 

 rectae. The high interstitial content of protein, as 



revealed by analysis of lymph (177) and the slow 

 apparent flow of plasma through the vasa recta 

 system [T-1824 transit time of 27.7 sec in the medulla 

 as compared to 2.5 sec in the cortex (166)] are in 

 support of this hypothesis. 



Recently, strong evidence of a countercurrent 

 system for water has been advanced by Morel et al. 

 (218). They compared the kinetics of distribution of 

 Na 22 and tritiated water in the kidneys of oliguric 

 hamsters. The concentration of the tracer in tissue 

 samples removed at graded levels from cortex to 

 papilla was measured. Na' 22 showed uniform distribu- 

 tion in less than 2 min, but the turnover of water in 

 the deepest regions of the kidney was not complete in 

 10 min. This they attributed to the passage of water 

 across the descending and ascending branches of the 

 loops of Henle and vasa recta. Thus, the osmotic 

 gradients of the hairpin system may supply the trigger 



